This invention relates to reclosable extruded plastic fasteners of the kind having interlockably cooperative fastener strips which are suitable for convenient manipulation into closed and open modes, and according to the present invention will thoroughly resist unintended opening due to twisting of the fastener assembly.
Heretofore, extruded plastic reclosable fasteners having complementary interlockable hook profiles have been successfully developed for wide ranging market utility.
One popular form of such reclosable fasteners has been the type wherein an essentially arrow-shaped profile is interlockably engagable in a complementary groove-shaped profile. While numerous patents disclosing this type of fastener could be listed, U.S. Pat. No. 3,808,649 has been selected as representative. While, in general, this type of fastener is of the readily manipulatable type for opening and closing, U.S. Pat. No. 3,808,649 combines the readily closing manipulation feature with permanent closure requiring either destruction or assistance of a tool for opening the fastener.
Extruded plastic fasteners of the kind to which the present invention is especially directed are represented in U.S. Pat. Nos. 3,633,642 and 3,886,633, wherein complementary fastener strips have monohook profiles which snap together and are held against unintentional displacement by backup flanges. In the fasteners disclosed by these patents, the interlocking hooks are relatively short and have reinforced fairly massive crown structure so that due to the relatively stiff action of the hooks, the backup flange structure as well as the profile stems must flex substantially both when snapping the fastener strips together and when separating the fastener strips.
A problem that has been encountered with respect to fasteners of especially the form shown in U.S. Pat. No. 3,633,642 resides in that under twisting conditions, the hook profiles of the fasteners may tend to release, and the fastener thus be unintentionally opened. It is to the alleviation of this problem that the present invention has been devised.